Panax ginseng C. A Meyer is a plant grown in the fair east of Asia (Northern latitude 33-48: Korea, North Manchuria—a part of Russia) and it belongs to Araliaceae Panax according to the plant taxonomy. In particular, ginseng grown in Korea is called Korean ginseng and is known to have excellent pharmaceutical properties. Ginseng products are classified into undried ginseng, red ginseng, white ginseng and Taeguk ginseng according to the preparation process.
Ginseng is known to have good preventive and medical effects for various adult health conditions such as arteriosclerosis, hypertension, stress, fatigue, stamina decrease, hypertension, climacteric diseases, diabetes mellitus, cancer, aging, etc. Nutrition 16(5), 391-392(2000); European Journal of Clinical Pharmacology, 55(8), 567-575(1999).
In industry, ginseng is extracted using solvents such as hot water or alcohols. Ginseng residue, which is a by-product of extracting ginseng, is a kind of dietary fiber consisting of polysaccharides. Even though ginseng residue has the potential to be used as dietary fiber material with various physiological properties, it has been widely used as animal feed or simply discarded.
Dietary fiber consisting of various non-starch polysaccharide components such as cellulose, hemicellulose, pectin, etc. is not digested by human enzymes. The most important factor which determines physiological activity of dietary fiber is solubility (Food Technology, 41(2), 81-85(1987)). Dietary fiber is classified into water-insoluble dietary fiber and water-soluble dietary fiber. Water-insoluble dietary fiber exhibits physiological functions such as increasing the size of excrement, reducing the time required for digested food to pass through the intestines, inhibiting starch hydrolysis, delaying glucose absorption, etc., which is attributed to a large amount of water absorption when water-insoluble dietary fiber passes through digestive organs. In contrast, a three-dimensional gel structure constructed by water-soluable dietary fiber delays the passage of food and prevents absorption of glucose. In particular, it is well known that water-soluble dietary fiber functions to decrease blood cholesterol levels.
Oligosaccharides are carbohydrates with low molecular weight and are classified into two groups according to the method used to produce them. Oligosaccharides such as isomalto-oligosaccharides, fructo-oligosaccharides, galacto-oligosaccharides, etc. are prepared by enzymatic bioconversion of sugars, while inulin oligosaccharides, alginate oligosaccharides, chitosan oligosuccharides, etc. are produced by hydrolysis of polysaccharides (Food Industry and Nutrition 3(1), 18-23(1998)).
Oligosaccharides are physiologically active as a bifidogenic factor that accelerates proliferation of useful intestinal microbes. Oligosaccharides produced by hydrolysis of polysaccharides have various physiological and pharmaceutical functions such as decreasing blood cholesterol levels, killing bacteria, activating the immune system, preventing/inhibiting cancer, etc. (Lebensm. Wiss. Technol., 27, 1-9(1996); Tren. Food Sci. Technol., 7, 353-368(1996)).
A plant cell wall is composed of polysaccharides such as cellulose, hemicelluloses, pectin, etc., lignin and glycoproteins. In most cases, these components do not exist in a free state but exist in a water-insoluble state because of strong covalent, hydrogen and ionic bonds (Korea Nutrition and Food Society, 23(2): 358-370(1994)). The solubilization of a plant cell wall structure existing in a water-insoluble state augments the content of water-soluable dietary fiber, which improves physiological characteristics of dietary fiber.
Conventionally, the insoluble dietary fiber components in a plant cell wall can be hydrolyzed by acid or alkali solution at a high temperature. However, this chemical hydrolysis method has various industrial problems such as generation of waste water, container corrosion, generation of unusable residues, structural damage of the cell wall component, etc. (Carbohydrate Research, 260, 283-296(1994)).
Therefore, there is need for the development of an environment-friendly solubilization process to produce functional carbohydrate materials from the walls of plant cells. Mechanical or enzymatic solubilization methods are good alternative ways to solubilize plant cell walls without using chemical treatments.
An example of a mechanical solubilization method is an extrusion process. An extruder simultaneously performs a variety of processes such as mixing, cooking, texturizing, drying, sterilizing, cooling, etc. in a single apparatus. The extrusion process, providing high temperature, high pressure and high shear force, is commonly used for manufacturing animal feed and processed food products such as noodles, cereals, etc.
The high shear force provided during the extruding process can also be effectively used for mechanically solublizing the water-insoluble polysaccharide components in the plant cell walls (Journal of Food Science, 63(5), 841-844(1998)). However, the technology to solubilize water-insoluble plant cell walls by the extruding process has not yet been fully developed. In particular, the extruding process for solubilizing insoluble ginseng cell walls has not yet been applied in industry.
An enzymatic solubilizing method can also be used to effectively solubilize the polysaccharide components of plant cell walls using polysaccharide hydrolytic enzymes. Ginseng residue consists mostly of polysaccharides, so it is very possible to produce oligosaccharides with low molecular weight by polysaccharide hydrolysis of ginseng residue. Ginseng polysaccharides are composed of cellulose, hemisellulose and pectin, and thus the hydrolysis of ginseng polysaccharides can be readily accomplished by using cellulase, hemicellulase, pectinase, etc.
Since polysaccharide hydrolytic enzymes such as cellulose, hemicellulase, and pectinase are commercially available, the enzymatic hydrolysis of polysaccharides can be applied easily for industrial purposes. In particular, since these commercial enzymes are composed of various complex enzymes, they can be more effectively used for the hydrolysis of plant cell walls consisting of complex polysaccharides.
Thus, the present invention is achieved by producing water-soluble dietary fiber from ginseng residue by an extruding process that combines high shear force, high temperature and high pressure, and also by producing ginseng oligosaccharides with low molecular weight from the ginseng residue using polysaccharide hydrolytic enzymes.
Accordingly, it is an object of the present invention to provide a method for producing dietary fiber economically from ginseng residue using an extruder without chemical treatment, and ginseng dietary fiber prepared by the extruding process.
It is another object of the present invention to provide a method for preparing oligosaccharides with low molecular weight from ginseng residue by polysaccharide hydrolysis, and ginseng oligosaccharides prepared by polysaccharide hydrolytic enzymes.